feat: implement client-side macro text storage and execution

Macros in WoW are client-side — the server sends only a macro index via
SMSG_ACTION_BUTTONS, never the text. This commit adds local storage and
a UI so macro slots are actually usable.

- GameHandler: getMacroText/setMacroText accessors backed by macros_ map;
  text is persisted to the character .cfg file as macro_N_text= entries
- Action bar left-click: MACRO slot executes first line of macro text as
  a chat/slash command (same path as /cast, /use, etc.)
- Context menu: "Execute" and "Edit" items for MACRO slots; "Edit" opens
  a multiline modal editor (320×80 px, up to 255 chars) with Save/Cancel
- Tooltip: shows macro text body below the index; hints "right-click to
  Edit" when no text is set yet

include/ui/game_screen.hpp

@@ -201,6 +201,10 @@ private:
     // Keybinding customization
     int pendingRebindAction = -1;  // -1 = not rebinding, otherwise action index
     bool awaitingKeyPress = false;
+    // Macro editor popup state
+    uint32_t macroEditorId_   = 0;        // macro index being edited
+    bool     macroEditorOpen_ = false;    // deferred OpenPopup flag
+    char     macroEditorBuf_[256] = {};   // edit buffer
     bool pendingUseOriginalSoundtrack = true;
     bool pendingShowActionBar2 = true;   // Show second action bar above main bar
     float pendingActionBarScale = 1.0f;  // Multiplier for action bar slot size (0.5–1.5)